Jar
n.) In deep well boring, a device resembling two long chain links, for connecting a percussion drill to the rod or rope which works it, so that the drill is driven down by impact and is jerked loose when jammed.
n.) In deep well boring, a device resembling two long chain links, for connecting a percussion drill to the rod or rope which works it, so that the drill is driven down by impact and is jerked loose when jammed.